A deaerating hollow fiber module manufactured according to the present invention can be used for example for: deoxygenated water for boiler feed water; super deaerating such as deoxygenation, decarbonation, denitrification, and the like in an ultrapure water production stage in a semiconductor manufacturing process; deaerating of resist solution and developer in a lithography process; rusty water deaerating for buildings, condominiums and the like; deaerating of water for medical treatment; deaerating and defoaming of jet ink; and so forth.
Recently, with the even higher accuracy of ink jet printers, a deaerating hollow fiber module for deaerating and defoaming (removing bubbles in the ink) from a liquid such as jet ink is demanded. Regarding deaerating and defoaming of ink, for example Patent Documents 1 and 2 disclose a deaerating hollow fiber module of a so called internal perfusion type that deaerates by feeding ink to inside a hollow fiber and then reducing the pressure on the outside of the hollow fiber.
Furthermore, in general deaeration, for example in the following Patent Documents 3 and 4 and so forth, it is disclosed that a so called external perfusion type where a liquid is flowed in contact with the outside of a hollow fiber, and the pressure is reduced inside the hollow fiber, is superior in dissolved gas removal performance. In the case of the external perfusion type, while supplying ink containing bubbles to the deaerating hollow fiber module so that it touches with the outside of the hollow fiber, the inside of the hollow fiber is evacuated. The bubbles contained in the ink pass through the membrane due to the pressure difference between the inside and outside of the hollow fiber, and are removed to the low pressure side. The ink from which the bubbles have been removed, is discharged from the module without passing through the hollow fiber.
In the case of deaerating the jet ink, either of these methods may be used. However from the point of deaerating efficiency and pressure loss per unit membrane area, the external perfusion type is more preferably used compared to the internal perfusion type.
For the hollow fiber used in the present invention, the material, the membrane form, and the membrane structure are optional provided it is a membrane in hollow fiber form which passes gas but does not pass liquid, and a hollow fiber that is used in a conventional deaerating hollow fiber module can be used. Examples of the material for the hollow fiber include, a polyolefin resin such as polypropylene, poly (4-methylpentene-1), or the like, a silicon fiber resin such as polydimethylsiloxane, and a copolymer thereof, and a fluorine-based resin such as PTFE, polyvinylidene fluoride, and the like. For the form of the sidewall (membrane) of the hollow fiber, any one of; a porous membrane, a micro porous membrane, or a homogeneous membrane (nonporous membrane) not having porosity can be used. As the membrane structure, either one of; a symmetric membrane (homogeneous membrane) where a chemical or physical structure of the overall membrane is homogeneous, or an asymmetric membrane (nonuniform membrane) where the chemical or physical structure of the membrane differs depending on the part of the membrane, can be used. The asymmetric membrane is a so called nonuniform membrane being a compact layer of a nonporous membrane and a membrane having porosity. The compact layer may be a surface portion of the membrane, or a portion inside the porous membrane, and it does not matter where the compact layer is formed within the membrane. This nonuniform membrane also includes a so called composite membrane in which the chemical structures are different, and a multi-layered structure membrane such as a three layer structure. In particular, since the nonuniform membrane that uses the poly (4-methylpentene-1) resin has a compact layer that blocks liquid, then it is particularly desirable for deaerating liquid other than water, for example ink. Furthermore, in the case of a hollow fiber used for the external perfusion type, then preferably the compact layer is formed on the outside surface of the hollow fiber.
The conventional deaerating hollow fiber module, as indicated for example in the following Patent Documents 6, 7, and 8, has a cylindrical core, and a multiplicity of hollow fibers bundled around the core. The cylindrical core ensures the rigidity of the deaerating hollow fiber module, and functions as a base for holding the multiplicity of hollow fibers at the time of manufacturing the module. Furthermore, it also has a role as a liquid supply passage for controlling the flow of liquid, however it also becomes a cause of pressure loss.    Patent Document 1: Japanese Unexamined Patent Application, First Publication No. H05-17712    Patent Document 2: Japanese Unexamined Patent Application, First Publication No. H10-298470    Patent Document 3: Japanese Unexamined Patent Application, First Publication No. H02-107317    Patent Document 4: Japanese Unexamined Patent Application, First Publication No. H05-245347    Patent Document 5: Japanese Unexamined Patent Application, First Publication No. H05-245348    Patent Document 6: Japanese Unexamined Patent Application, First Publication No. S52-99978    Patent Document 7: Japanese Unexamined Patent Application, First Publication No. 2002-361050    Patent Document 8: Japanese Unexamined Patent Application, First Publication No. 2005-305432